Abstract

A coupled electron-ion transfer reaction at thin
organic-film-modified electrodes (TFE) is studied in the presence of glucose oxidase (GOx) under voltammetric conditions. TFE consists of a graphite electrode modified with a nitrobenzene solution of decamethylferrocene (DMFC) as a redox mediator and tetrabuthylammonium perchlorate as an organic-supporting electrolyte, in contact with aqueous buffer solutions containing percholarte ions and GOx. The redox turnover of DMFC coupled with perchlorate transfer across water|nitrobenzene interface composes the coupled electronion transfer reaction. Glucose oxidase strongly adsorbs at the liquid|liquid interface affecting the coupled electron-ion transfer reaction by reducing the surface area of the liquid interface,
prompting coadsorption of the transferring ion and lowering
down slightly the rate of the ion transfer reaction. Although the enzyme exists as a polyvalent anion over the pH interval from 5.6 to 7, it does not participate directly in the ionic current across the liquid interface and percholrate remains the main transferring ion. Raman spectroscopic data, together with the voltammetric data collected by three-phase droplet electrodes, indicate that the adsorption of the enzyme does not depend either on the redox mediator (DMFC) or the organicsupporting electrolyte, while being driven by intrinsic interactions of the enzyme with the organic solvent. The overall electrochemical mechanism is mathematically modeled by considering linear adsorption isotherm of the transferring ion, semi-infinite mass transfer regime, and phenomenological second-order kinetic model.